Keratins are a class of structural proteins widely represented in biological structures, especially in epithelial tissues of higher vertebrates. Keratins may be divided into two major classes, the soft keratins (occurring in skin and a few other tissues) and the hard keratins (forming the material of nails, claws, hair, horn, feathers and scales).
The toughness and insolubility of hard keratins, which allow them to perform a fundamental structural role in many biological systems, are desirable characteristics found in many of the industrial and consumer materials derived from synthetic polymers. In addition to possessing excellent physical properties, keratin, as a protein, is a polymer with a high degree of chemical functionality and consequently exhibits many properties that synthetic polymers cannot achieve. Keratin is therefore, well suited for use as a base for the development of naturally derived products as an alternative to completely synthetic materials.
Materials in the form of films, membranes coatings and fibers derived from synthetic polymers are commonly used in a wide variety of applications. This is due in large part to the wide range of desirable properties that the materials possess, both in terms of performance in a particular application and processing to create a desired form or shape. The use of materials developed from natural polymers or biopolymers such as cellulose, chitin, chitosan, keratin, alginate, zein and starch is much less extensive (Matsumoto, et. al., J. Appl. Polym. Sci. 60 (1996), 503); (Yang, et. al., J. Appl. Polym. Sci. 59, (1996), 433; Cates, et. al., 21 (1956), 125, Schmpf, et. al., Ind. Eng. Chem. Prod. Res. Dev., 16 (1977), 90). This is due in part to the narrower range of performance properties natural polymers posses, making them only suitable for certain applications, as well as more limited processing characteristics when compared to synthetic materials. It is, therefore, desirable to improve the natural material characteristics through combination and modification.
Hydrolysed keratin has been used as a base for graft copolymerisation (Sastry, T. P., C. Rose, et al. (1997). “Graft copolymerization of feather of feather keratin hydrolyzate: preparation and characterization.” Journal of Polymer Materials 14(2): 177-181), however, the nature of a hydrolysate is such that many of the core characteristics of the original protein are lost, and the properties of the resulting modified materials are not as desirable as they could be if the characteristics of the original protein are maintained. This is achieved in the present invention which targets intact proteins as the base for modification. Intimately blended polymer mixtures have been utilised to create materials containing keratin, for example with other biopolymers such as chitin (Tanabe, T; Okitsu, N; Tachibana, A and Yamauchi, K, Biomaterials, 23, 3, 817-825 2002) and synthetic polymers such as polyvinyl alcohol (Kazunori, K., Mikio, S., Toshizumi, T. and Kiyoshi, Y.; J. Appl. Polym. Sci., 91 (2004), 756-762, Sakurada, I; Polyvinyl alcohol fibers; Marcel Dekker: New York, 1985). However, as with previous work on chemical modification of keratin, hydrolysates have been used as the base keratin material. Intact keratin protein fractions are used as the base material in the present invention, a strategy employed to maximise the transfer of desirable characteristics from the keratin source to the final product.
Keratin fibres, such as human hair, wool and other animal fibres, consist of a complex mix of related proteins that are all part of the keratin family. These proteins can be grouped according to their structure and role within the fibre into the following groups:                the intermediate filament proteins (IFP), which are fibrous proteins found mostly in the fibre cortex;        high sulfur proteins (HSP), which are globular proteins found in the matrix of the fibre cortex, as well as in the cuticle.        high glycine-tyrosine proteins (HGTP), found mostly in the fibre cortex.        
The ultrastructure of keratin fibres is well known in the art, and discussed in detail by R. C. Marshall, D. F. G. Orwin and J. M. Gillespie, Structure and Biochemistry of Mammalian Hard Keratin, Electron Microscopy Reviews, 4, 47, 1991. In the prior art described in which keratins are used as a base for chemical modification, the keratin utilized is hydrolysed as one material and no attempt is made to maintain the molecular weight of the protein. Further no attempt is made to fractionate the keratin source into its constituent components. As a result of protein hydrolysis, many of the desirable properties of the proteins are lost. Low molecular weight keratin peptides aggregate with a much lower degree of order to produce materials with much poorer physical properties than the high molecular weight keratins from which they are derived. In addition, irreversible conversion of cysteine as may occur with chemical methods of keratin decomposition, yields a peptide product that has lost the core functionality that that distinguishes it from other protein materials. Particular keratin protein fractions, for example keratin intermediate filament proteins, offer the potential to capture desirable material characteristics for which keratin has been evolved, even further if the proteins are kept intact.